Patients with familial hypercholesterolemia (FH) are at high risk of premature coronary artery disease due to elevated low density lipoprotein (LDL) and Lp (a) cholesterol levels. Diet and drug therapy can reduce cholesterol concentrations in most patients with heterozygous FH, but a small proportion of heterozygous and nearly all homozygotes do not respond to therapy. Selective removal of LDL by dextran sulfate affinity adsorption was evaluated in these patients in a collaborative multicenter U.S. Study. The dextran sulfate apheresis system (Liposorber LA-15 Kanegatuchi, Japan) removed LDL and Lp(a) without affecting HDL or albumin concentrations, thus allowing return of autologous plasma and avoiding the need for colloid replacement solutions. Three homozygous and three heterozygous FH patients were enrolled at the Clinical Center; the total cohort enrolled nationwide included 10 homozygotes and 54 heterozygotes. The study is now complete and closed to further accrual of patients, although those having achieved documented benefit are permitted to continue LDL-apheresis treatments on an exemption basis granted by the FDA, pending device licensure. Treatments were administered in 7 to 14 day intervals. Mean acute reductions in total, LDL, and Lp (a) cholesterol levels were 70%, 81% and 68% respectively in homozygotes and 61%, 76% and 65% respectively in heterozygotes. Time-averaged levels of LDL cholesterol were reduced 53% *(447 to 310 mg/dl) in homozygous FH patients and 41% (243 to 143 mg/dl) in heterozygous ones. The treatments we well tolerated and no significant adverse reactions occurred. Our data suggest that dextran sulfate adsorption is a safe and effective way to clear plasma of LDL cholesterol, and has advantages, compared to simple plasma exchange, of eliminating the need for colloid replacement solutions and promoting a more beneficial LDL/HDL cholesterol ratio. The IDE number for the investigational device used in this study is G880069; the IDE holder is Kaneka America.